Investigations of the functional properties of neurosecretory cells in the supraoptic nucleus of the hypothalamus have been principally concerned with osmotic and CNS stimulations. Studies of ADH levels in plasma have been more involved with cardiovascular stimuli. It is the aim of this proposal to study the electrical activity of SON cells which can and cannot be antidromically stimulated from the neurohypophysis in response to several stimuli known to alter ADH release. It is important to define the dominant stimulus to these neurons and to the extent possible how the various stimuli interact. This will be accomplished by: 1) obtaining baseline data of the normal firing rates of SON neurons which can and cannot be antidromically activated; 2) observing the response of these cells to alterations of blood volume, intravascular pressures in various segments, blood osmolarity, PO2, and PCO2 in their receptor areas: 3) applying two or more of the above stimulations simultaneously. Information gained from this study should be useful in investigations of experimentally less accessible neuroendocrine systems. Knowledge of the response characteristics of these cells is important to our understanding of diseases involving water and electrolyte imbalances and posibly irregularities in systemic blood pressures.